The present application relates to III-N-type power devices, methods, and systems, and more particularly to III-N-type integrated power devices having heterostructure transistors and lateral field-effect rectifiers on the same chip, and to related manufacturing methods, operating methods, and systems.
Note that the points discussed below may reflect the hindsight gained from the disclosed inventions, and are not necessarily admitted to be prior art.
Power semiconductor devices include two categories: 1) three-terminal transistors as switches and 2) two-terminal rectifiers. Both rectifiers and transistors are essential components in high voltage power electronics applications, for example, switching-mode power supplies and many forms of drive circuits.
For transistors, AlGaN/GaN high electron mobility transistors (HEMTs) are often the best choice. Group III-nitride (“III-N”) compound semiconductors, such as those incorporating AlGaN/GaN, possess the advantages of having wide bandgap, high breakdown field, and large thermal conductivity, which can bring significant benefits to the design of heterostructure field-effect transistors and applications. The wide-bandgap AlGaN/GaN heterostructure system, enhanced by the spontaneous and piezoelectric polarization effects, yields two-dimensional electron gas (2DEG) channel with a high sheet charge concentration and high electron mobility. HEMT transistor structures hence generate record output power densities at microwave frequencies.
AlGaN/GaN heterostructures for power electronics application can operate at higher temperature and higher switching frequency than other device types. For a given breakdown voltage (BV) requirement, the GaN semiconductors may present an on-resistance (Ron) that is three orders of magnitude lower than Si semiconductors.
For rectifiers, two-terminal power rectifiers with low forward turn-on voltage (VF,ON), low specific on-resistance (RON, sp) and high reverse breakdown voltage (BV) are desirable in high-voltage power electronics, e.g. in switching-mode power supplies and power factor correction circuits. Low on-state resistance and short reverse recovery time, for a given off-state breakdown voltage, are important for power conversion efficiency.
Various efforts have been made to improve power rectifier performance. Some proposed structures include JBS (junction barrier Schottky) diode, MPS (merged p-i-n Schottky) diode, and synchronous rectifier. Another is Schottky barrier diodes (SBDs, FIG. 1) and p-i-n diodes on doped bulk GaN, which presents high-breakdown low-on-resistance features.
However, since the epitaxial structures for SBD or p-i-n diodes are not compatible with the HEMT structures, the SBD or p-i-n diode rectifiers have not been successfully integrated with HEMTs (at least not without unacceptable performance loss). Although SBDs can be directly formed on AlGaN/GaN heterostructures, the series combination of the AlGaN/GaN heterojunction with the metal-AlGaN Schottky barrier results in higher turn-on voltages and higher on-resistances.
A recently developed dual-metal SBD system (FIG. 2) combines a low Schottky barrier metal (Al/Ti) and a high Schottky barrier metal (Pt) to provide an anode with a low turn-on voltage. However, this too presents some incompatibility with AlGaN/GaN HEMTs, since the HEMTs conventionally use Ni/Au gate metallization. Thus additional processing steps will be required.